Virtually all modern vehicles, autos, vans and trucks have air bag deployment systems. An increasing fraction of the air bag deployment systems currently available include a passenger-side air bag as well as a driver-side air bag.
However, a passenger-side air bag deployment system presents problems in regard to criteria for deployment. That is, it is not simply an issue of always deploying a passenger air bag, as injury to occupants can occur by deployment in certain situations. For example, the air bag should deploy only if an occupant is in fact in the passenger seat, and not when the seat is empty. An even more important problem is the danger of deploying a passenger side air bag when it has a rear-facing child seat (RFCS). The deployment of an air bag against the back portion of an RFCS occupied by a child can cause serious injury to the child by catapulting the child into the back of the car seat, thus defeating the safety advantages of both the air bag and the RFCS during a collision.
Accordingly, it is very important to provide a means for determining when the passenger seat is occupied and when it is not occupied. It is even more important to determine the classification of the "object" in the seat, including when it is occupied by a child in a RFCS so that such information can be used to prevent deployment of the air bag for an RFCS occupancy state. Any means for determining the nature and status of an occupant, including the presence and orientation of a child seat, must be highly reliable in order to signal selective deployment of the air bag when the seat is occupied by a passenger and prevent deployment of the air bag when the seat is occupied by an RFCS. This is compounded by the fact that there are over thirty-five different infant seats available. The seats are adjustable, and the interior configuration and buckling arrangement of each vehicle is different.
Thus, it is no easy task to provide a sensor system, meaning sensor units and methods of operation and signal processing, to reliably detect change of state from an empty to an occupied seat and determine the nature (classify), position (location) and/or orientation of an object or passenger in the vehicle. By way of example, if a thermal sensor is used, its reliability may be reduced by thermal conditions within the vehicle which can change dramatically with the seasons, weather, vehicle interior configuration, rapidly changing exterior shading, passenger clothing and/or size, driver's choice of interior climate, smoking, activity, hot food (e.g., pizza) on the seat, etc. Thus, a thermal sensor acting alone can lead to falsely declared occupant presence, and more importantly, failure to detect the presence of an occupant. Furthermore, there may be cases where the thermal signature of an RFCS blends so well with the seat upholstery that a thermal sensor does not see it, allowing the air bag system to deploy despite the presence of a child-occupied RFCS.
Conversely, if one were to use instead distance measurements, such as by the use of acoustic sensors, such sensor must be capable of distinguishing between the presence of an RFCS and the presence of a passenger holding an object, being in a position or making a motion which can result in distance measurements which mimic the presence of an RFCS.
There are other scenarios as well that require a sensor system to recognize, classify and signal air bag controllers to take appropriate action, such as an FFCS, inanimate objects, a passenger holding an inanimate object, an out-of-position passenger, and so on.
In addition to these basic sensor requirements, the system for determining the presence of a passenger in the passenger seat and the presence or absence of a rear-facing child seat, must be cost effective and must be in a sufficiently small package to prevent interference with normal vehicle operation. Such systems must be compatible with the aesthetics of the vehicle so as not to affect a vehicle's salability particularly as it relates to new passenger cars. Furthermore, the cost of installing such system in the vehicle must remain simple to keep manufacturing cost low. Preferably, all the sensors should be kept in a single unit to ease the assembly of the vehicle in production or retrofitting older vehicles.
There is no currently available sensor system known to the Applicants which can reliably distinguish the presence, absence and nature of an object or a passenger in the passenger seat. None today can selectively distinguish the presence or absence of a rear-facing child seat in the passenger seat.
There is also no currently available sensor system that can account for a wide variety of possible variations in both thermal and distance parameters that are encountered in the actual wide range of circumstances of occupancy, nor one that is sufficiently versatile to be adaptable to the wide range of vehicle interior configurations.
An example of a system for actuating a driver air bag restraint is shown in White et al U.S. Pat. No. 5,071,160 (Automotive Systems Laboratory) which employs an ultrasonic acoustic sensor for sensing the position of the driver, a "pyrotechnic" sensor for sensing the presence of the driver, and a pressure transducer within the seat to sense the approximate weight of the driver and an air bag control module to trigger deployment of the air bag. As best understood, when an impending crash is sensed by a crash sensor, a control module samples the sensed position of the passenger at fixed time intervals to calculate the rate or movement of the passenger relative to the various fixed motion structures of the vehicle. This rate of relative passenger movement is used to corroborate the acceleration data from the crash sensor and ensure deployment of the air bag where the passenger is at substantial risk of injury. That is, the interior passenger acceleration is apparently used to prevent false crash signals from the crash sensor. Crash sensors may trigger air bag deployment during a minor bump in close slow moving traffic or during parking. This "is-the-passenger-being-accelerated-at-the-same-time" system is directed to correcting false crash sensor signals.
The patent describes the desired results but does not detail the process or circuitry to achieve these results beyond stating that the air bag control circuit uses error correction methods such as a plurality of each type of sensors (crash sensor, pyrotechnic, ultrasonic, acoustic, and pressure transducer) for each assigned monitoring task to prevent falsing. Accordingly, the control circuit is said to employ redundant sensors for each monitoring task and the instructions executed by the control module are said to include error correction subroutines known to one skilled in the art. A dashboard signal lamp can be lit when the air bag effectiveness is too low, or the likelihood of passenger injury by the air bag is greater than the injury if he hit the steering wheel, dash or knee bolster, the latter being consistent with the slow bump situation described above.
Accordingly, there is a need in the art for a reliable occupant sensor system for use in conjunction with vehicle air bag deployment systems. There is also a need for a sensor system that can meet the aforementioned requirements for reliability in detecting the presence, absence and classification of an object, a passenger or RFCS in a wide range of circumstances, irrespective of whether a passenger is holding an object and irrespective of the thermal conditions that may be found in the vehicle. Such a sensor system must also be a cost effective component of the vehicle that does not detract from the aesthetics of the vehicle interior or unduly increase the cost of manufacturing or assembling a vehicle.